1. Field of the Invention
This invention relates to supermolecular structures that are used to build semiconductor devices. More specifically, this invention relates to structures and devices based on the controlled discrete distribution and arrangement of single impurity dopant atoms or molecules within a lattice or amorphous matrix. The controlled arrangement of dopants in a semiconductor matrix provides structures that exhibit very beneficial characteristics by engineering single-charge effects. The invention also relates to methods of manufacturing such structures and devices.
2. Description of the Problem
There exists a need for the ability to control and order the distribution and effect of impurities, eg. dopant atoms, in a lattice or semiconductor matrix. Such an ability would open new opportunities to making ‘smart’ nanoelectronic structures. Today's semiconductor based microelectronics relies on device structures with stochastic distributions of dopants. Conventional doping is treated as a macroscopic phenomenon, as it adds large numbers of atoms to semiconductor materials. It would be advantageous to develop structures that represented the ultimate limits of doping and host material control.
For large numbers of atoms, the typical behavior and distribution of these atoms is governed by Boltzman or Fermi-Dirac statistics. From this stochastic perspective, doping effects a shift of Fermi level states. These states are dependent on temperature, dopant concentration, and semiconductor band gap. FIG. 1 illustrates pn-junction barrier height as a function of band gap and Fermi level position. The Fermi level position corresponds to a dopant concentration. In this macroscopic case, the addition or subtraction of one to a few extra dopant atoms or electrons to the system does not induce a significant change to the potential distribution. In FIG. 1, NB is the potential barrier height in a pn-junction, Eg is semiconductor band gap, EFd and EFa are Fermi levels in respectively acceptor-doped and donor-doped parts of semiconductor, Na, Nd are volume concentrations of acceptors and donors, respectively, such that, NB=Eg−(EFn+EFP). For a complete discussion of doping effects, see the book by S. M. Sze, Physics of Semiconductor Devices, (1981, Johne Whiley & Sons, Inc.), which is incorporated herein by reference.
Conventional scaling of semiconductor devices to smaller and smaller sizes fundamentally will become limited by the macroscopic behavior described above. As devices become smaller and smaller, the numbers of dopant atoms in a device or region of interest also continues to decrease. At some point, the number of dopants in the active areas become so small that performance will be dominated by small number effects and will no longer be controlled sufficiently by the stochastic distributions of dopants. Using conventional semiconductor manufacturing methods in this small number domain, the properties of the device become unpredictable and uncontrollable. It would be desirable to tightly control the distribution and placement of dopant atoms in a material by atomic level engineering, such that the behavior of the material can be predicted by leveraging single charge effects.